The present invention relates to a belt for a continuously variable transmission (CVT) which is constituted of a metal ring assembly and a plurality of metal elements, and a method of producing each of the metal elements of the CVT belt.
FIG. 6 illustrates a part of an endless CVT belt of a related art, which includes metal element 1 and metal ring assembly 10 supporting metal element 1 thereon. Metal ring assembly 10 is indicated by a phantom line, which is formed by a plurality of metal rings laminated one on another. Each of the metal rings is made of a thin metal sheet. Metal element 1 is formed by subjecting a workpiece to presswork and then to deburring and heat treatment. The workpiece is made of a metal sheet. Metal element 1 includes body 2, head 4 with ears 6, and neck 3 connecting head 4 to body 2. Body 2 includes saddle portions 5 which are disposed on an upper portion thereof and spaced from each other in a lateral direction perpendicular to a circumferential direction of the CVT belt. Body 2 includes a lower portion having a thickness which gradually decreases in a downward direction such that metal element 1 is inclinable forward or rearward in a traveling direction of the CVT. Neck 3 is disposed between saddle portions 5. Metal element 1 includes two slots 7 respectively disposed between saddle portions 5 and ears 6. Each of slots 7 is partly defined by saddle surface 5A of saddle portion 5. Metal ring assembly 10 is engaged in each of slots 7. Engaging projection 8 is formed on a central portion of head 4 as shown in FIG. 6. Engaging projection 8 defines projecting portion 8A on one side face of head 4 and recessed portion 8B on an opposite side face thereof as shown in FIGS. 2A–2C. A plurality of metal elements 1 are arranged in array in the circumferential direction of the CVT belt to form an annular shape as a whole. In the arrangement, projecting portion 8A of engaging projection 8 of metal element 1 is engaged with recessed portion 8B of engaging projection 8 of adjacent metal element 1. Neck 3 is disposed in a space between metal ring assemblies 10. The thus-constructed CVT belt is wound on a pair of pulleys of the CVT.
When the CVT belt passes by the pulleys during operation of the CVT, the adjacent metal elements are inclined forward or rearward in the traveling direction of the CVT belt. Due to the inclination of the adjacent metal elements, there occurs difference in height between the saddle surfaces. This will cause the inner circumferential surface of the metal ring assembly to be pressed onto front or rear ridges where the adjacent saddle surfaces encounter front and rear surface in the traveling direction of the CVT belt. Therefore, stress concentration will occur the mutual contact portion between the ridges of the respective saddle surfaces and the inner circumferential surface of the metal ring assembly.
Japanese Patent Application First Publication No. 2001-21007 (corresponding to European Patent Application First Publication No. 1067311 A1) discloses a metal element of a CVT belt which includes a saddle surface having curved portions on the opposed peripheries in a traveling direction of the CVT belt. The curved portions are formed by beveling such as barrel polishing. With the provision of the curved portions on the opposed peripheries of the saddle surface, the related art aims at reducing the stress concentration which occurs at the inner circumferential surface of the metal ring assembly when the adjacent metal elements comes into contact with the opposed peripheries of the saddle surface of each of the metal elements at an inclined state thereof upon passing by the pulleys. Owing to the reduction of the stress concentration, the related art aims at preventing deterioration of a life of the metal ring assembly.